以昇陳

The Spiro-BD-2OEG with composition-conditioning agent functionality is designed to improve the composition stability in the doped-Spiro-OMeTAD hole transport layer (HTL). By employing this strategy, the HTL shows a pinhole-free and smooth morphology with an enhanced Spiro-OMeTAD ordering. Finally, the resultant perovskite solar cells show an excellent power conversion efficiency of 24.19% and improved thermal, moisture, and operational stabilities.

Abstract

The doped Spiro-OMeTAD hole transport layer (HTL) formed using the lithium bis(trifluoromethane) sulfonimide salt and 4-tert-butylpyridine with phenethylammonium iodide surface treatment on a perovskite film has continuously dominated the record power conversion efficiencies (PCEs) of perovskite solar cells (pero-SCs). However, unstable HTL compositions and iodide salts can cause severe device degradation. In this study, an HTL composition-conditioning agent (CCA), Spiro-BD-2OEG, is designed, which contains a Spiro-OMeTAD-like backbone, functional pyridine units, and oligo (ethylene glycol) chains. This finely designed CCA presents good miscibility with Spiro-OMeTAD and its dopants and acts as a conditioning agent through weak bond interactions. As a result, the CCA-regulated HTL shows a pinhole-free and smooth morphology with enhanced Spiro-OMeTAD ordering and improves dopant stability. In addition, the gradient-distributed CCA in the HTL can narrow the energy level offset with the valence band of the perovskite. The resultant pero-SCs exhibit an excellent PCE of 24.19% without any interface treatment and weak size dependence. A remarkable PCE of 22.63% is obtained even for a 1.004-cm² device. Importantly, the strategy shows good universality and significantly promotes the long-term stability of the pero-SCs based on the classical doped Spiro-OMeTAD.

This review presents a comprehensive overview of the gaps between the materials-level coin cells and device-level pouch cells, mechanistic understanding and quantitative discussion for failure mechanisms of pouch-type Li metal anodes, and the recently proposed strategies to suppress dendrite growth in pouch cells.

Abstract

Lithium metal battery has been considered as one of the potential candidates for next-generation energy storage systems. However, the dendrite growth issue in Li anodes results in low practical energy density, short lifespan, and poor safety performance. The strategies in suppressing Li dendrite growth are mostly conducted in materials-level coin cells, while their validity in device-level pouch cells is still under debate. It is imperative to address dendrite issues in pouch cells to realize the practical application of Li metal batteries. This review presents a comprehensive overview of the failure mechanism and regulation strategies of Li metal anodes in practical pouch cells. First, the gaps between the scientific findings in materials-level coin cells and device-level pouch cells are underscored. Specific attention is paid to the mechanistic understanding and quantitative discussion on the failure mechanisms of pouch-type Li metal batteries. Subsequently, recently proposed strategies are reviewed to suppress dendrite growth in pouch cells. The state-of-the-art electrochemical performance of pouch cells, especially the cell-level energy density and lifespan, is critically concerned. The review concludes with an attempt to summarize the scientific and engineering understandings of pouch-type Li metal anodes and propose some novel insights for the practical applications of Li metal batteries.

Potassium-sulfur batteries as a newly emerged energy storage system require systematic fundamental understandings regarding their mechanisms and challenges. In this review, efforts have been devoted to comprehensively summarize the recent progresses in each component of potassium-sulfur batteries, including cathodes, anodes, electrolytes, separators, and binders. Perspectives on potassium-sulfur batteries are also provided for future development and applications.

Abstract

The potassium–sulfur battery (K–S battery) as an innovative battery technology is a promising candidate for large-scale applications, due to its high energy density and the low cost of both K and S. The development of the K–S technology is, however, inhibited by its low reversible capacity and the safety issues related to the K metal anode. Here, the review starts by discussing the mechanism of the redox reactions for the K–S batteries and emphasizes the challenges for this battery system based on its current research status. Furthermore, the current improvement strategies for the K–S system in terms of the sulfur cathode, electrolyte, separator, and K metal anode are summarized. Finally, future perspectives on the development of the K–S system are proposed.

Nature Chemistry, Published online: 27 October 2022; doi:10.1038/s41557-022-01070-4

Room-temperature phosphorescence in organic solids is attractive for practical applications but remains rare. Now, highly phosphorescent boroxine-linked covalent organic frameworks have been prepared by covalent doping with halogen atoms through the use of halogenated precursors. The resulting porous COFs exhibited oxygen-sensing capabilities with millisecond response time over a wide range of partial oxygen pressures.

An organic molecule PO-T2T is investigated as an electron transport layer (ETL) material for InP green quantum-dot light-emitting diodes (QLEDs). By replacing ZnMgO with PO-T2T, exciton quenching is suppressed and charge balance is improved, and thus the resultant QLEDs exhibit a maximum external quantum efficiency of 15.0% and a luminance of 10 010 cd m⁻², corresponding to 211% and 237% enhancements, respectively, compared to 7.1% and 4207 cd m⁻² of the devices with ZnMgO ETL.

Abstract

ZnMgO thin film is commonly used as an electron transport layer (ETL) in quantum-dot light-emitting diodes (QLEDs); however, it often induces the problems of interface exciton quenching and electron over-injection in the devices. Herein, an organic molecule 2,4,6-tris(3-(diphenylphosphoryl)phenyl)-1,3,5-triazine (PO-T2T) is investigated as a ETL material for InP green QLEDs. Due to the high injection barrier and moderate electron mobility, the PO-T2T can prevent electron over-injection and accumulation in the InP QLEDs. Besides, with the organic ETL, the interfacial exciton quenching is effectively suppressed. By depositing the PO-T2T using a solution-assisted evaporation method, efficient InP green QLEDs are achieved, which exhibit a maximum external quantum efficiency of 15.0% and a luminance of 10 010 cd m⁻², corresponding to 211% and 237% enhancements, respectively, compared to 7.1% and 4207 cd m⁻² of the devices with ZnMgO ETL.

The uniform Li₃PO₄ layer in place of Li₂CO₃ contaminant is in situ built on garnet surface by making use of the molten NH₄H₂PO₄ salt driven conversion reaction. The Li₃PO₄-modified layer enables the highly air-stable garnet electrolyte without Li₂CO₃ formation for even 20 days as well as the lithiophilic interface with dendrite-free Li deposition.

Abstract

Garnet-type electrolytes show great potential in application of solid-state lithium batteries due to their high ionic conductivity and wide electrochemical window. However, the formation of surface Li₂CO₃ derived from air exposure triggers uneven contact with Li-metal, leading to undesirable dendrite growth and performance deterioration. Herein, the Li₃PO₄ layer replacing Li₂CO₃ contaminant is built on garnet surface by taking molten NH₄H₂PO₄ salt driven conversion reaction. The high-flowability molten salt contributes to conformal formation of Li₃PO₄, realizing the air-stable garnet by preventing the re-attack of H₂O/CO₂ in air. Besides, the high work of adhesion for Li₃PO₄ on Li-metal along with the transformation from Li₃PO₄ to Li₃P/Li₂O when contacting with molten Li-metal enables a lithiophilic interlayer, leading to a seamless Li/garnet contact with ultralow interfacial resistance of 13 Ω cm². Such ion-conducting but electron-insulating layer regulates the uniform distribution of Li-flux, enabling a large critical current density of 1.2 mA cm⁻². Furthermore, the solid LiCoO₂/Li cell with the modified garnet delivers a discharge capacity of 130 mAh g⁻¹ at 30 °C, accompanied by a capacity retention of 81% after 150 cycles. This study proposes a promising solution for improvement of air stability and interfacial compatibility of garnet using facile molten salt treatment.

Engineering of donor–acceptor–donor functional enamine hole transporting materials is presented leading to the low-cost hole transporting materia V1359 to reach power conversion efficiency over 22% in perovskite solar cells with excellent stability surpassing the reference spiro-OMeTAD due to the incorporation of the malononitrile acceptor units that passivate the surficial perovskite defects via Pb–N interactions.

Abstract

In this study, a series of donor–acceptor–donor (D-A-D) type small molecules based on the fluorene and diphenylethenyl enamine units, which are distinguished by different acceptors, as holetransporting materials (HTMs) for perovskite solar cells is presented. The incorporation of the malononitrile acceptor units is found to be beneficial for not only carrier transportation but also defects passivation via Pb–N interactions. The highest power conversion efficiency of over 22% is achieved on cells based on V1359, which is higher than that of spiro-OMeTAD under identical conditions. This st shows that HTMs prepared via simplified synthetic routes are not only a low-cost alternative to spiro-OMeTAD but also outperform in efficiency and stability state-of-art materials obtained via expensive cross-coupling methods.

Via incorporating bandgap modulation and zwitterionic functionalization, the second near-infrared (NIR-II) excitation donor–acceptor–donor-based small molecule with high QY (0.65%) and great photothermal property (η = 30.8%) is successfully developed, which can be intercalated within liposomes and retain its excellent optical properties in an aqueous environment, realizing precise in vivo 1064 nm single-photon NIR-II fluorescence imaging/photothermal therapy.

Abstract

Conjugated small-molecule (CSM) phototheranostic agents that operate in the second near-infrared (NIR-II) region have garnered significant attention in the field of biomedicine. However, a lack of fluorescence-emitting ability hinders their use in precise fluorescence imaging (FI)-guided photothermal therapy (PTT). Herein, a two-pronged fluorescence intensification strategy—molecular engineering for rational bandgap modulation and lipid-intercalation to combat fluorescence quenching—is used to develop NIR-II-excited ultrabright donor–acceptor–donor-based (D–A–D)-based zwitterionic CSM nanoagent for tumor phototheranostics. The molecular engineering strategy produces the NIR-II-excited D–A–D-based zwitterionic fluorophore (BTFQ) that exhibits a high NIR-II fluorescence quantum yield (QY = 0.65%) in dichloromethane. More importantly, BTFQ complexed with liposome (DMPC) to form the zwitterion–liposome nanoagent (BTFQ/DMPC) shows a negligible loss of QY (0.63%) in aqueous media. Moreover, because BTFQ/DMPC possesses excellent photothermal conversion efficiency (PCE = 30.8%) performance, it can be used to realize efficient in vivo 1064 nm single-photon high-resolution NIR-II FI guided NIR-II PTT. This study introduces a new avenue for the development of NIR-II-excited NIR-II FI/PTT agents for precise and effective tumor treatment.

Organic planar heterojunctions are fabricated by matching the thickness of a non-fullerene acceptor to its exciton diffusion length. Additional hole transfer mediated by the exciton diffusion generates a photocurrent over 10 mA cm⁻² in the planar heterojunction. Well-defined planar interfaces reduce the dark leakage current, resulting in 83 times higher photodetector detectivity than the corresponding bulk heterojunction device.

Abstract

While non-fullerene acceptors (NFAs) have recently been demonstrated to exhibit long-range exciton diffusion, most organic photovoltaic and photodetector studies still focus on blended polymer: NFA systems. Herein, a 40 nm exciton diffusion length for IT4F excitons is determined, and it is demonstrated that sharp interface, planar heterojunction (PHJ) IT4F/PM6 devices with the IT4F layer thickness matched to this diffusion length yield optimized photovoltaic and photodetector performance. The PHJ devices yield an enhanced device open-circuit voltage relative to bulk heterojunction (BHJ) devices, associated with suppressed bimolecular recombination losses. The PHJ architecture also results in a ≈100-fold increase in electroluminescence (EL) quantum efficiency relative to the BHJ device, correlated with a shift from charge transfer state EL for the BHJ to IT4F exciton dominated EL for the PHJ, attributed to significant hole injection from PM6 into IT4F. Of particular note, the PHJ architecture is shown to suppress dark leakage current, resulting in 83 times higher photodetector detectivity at −2 V bias than the equivalent BHJ device.

This is a review on the design of purely organic small molecules to overcome the energy gap law and achieve highly efficient near-infrared light emission. Representative deep-red to near-infrared molecules reported over the past 5 years are introduced and analyzed. Promising molecular design strategies to achieve higher quantum efficiencies are also reviewed.

Abstract

Organic light-emitting materials in the near-infrared (NIR) region are important to realize next-generation lightweight and wearable applications in bioimaging, photodynamic therapy, and telecommunications. Inorganic and organometallic light-emitting materials are expensive and toxic; thus, the development of purely organic light-emitting materials is essential. However, the development of highly efficient NIR light-emitting materials made of organic materials is still in its infancy. Therefore, this review outlines molecular design strategies for developing organic small-molecule NIR light-emitting materials with high emission efficiency that can overcome the energy-gap law to be applied to next-generation wearable devices. After briefly reviewing the basic knowledge required for the NIR emission of organic molecules, representative high-efficiency molecules reported over the past 5 years are classified according to their core moieties, and their molecular design, physical properties, and luminescence characteristics are analyzed. Further, the perspective and outlook regarding the development of next-generation high-efficiency NIR organic light-emitting materials are provided.

Publication date: December 2022

Source: Materials Today Energy, Volume 30

Author(s): Devendrasinh Darbar, Thomas Malkowski, Ethan C. Self, Indranil Bhattacharya, Mogalahalli Venkatesh Venkatashamy Reddy, Jagjit Nanda

Nature Energy, Published online: 27 October 2022; doi:10.1038/s41560-022-01144-0

It is a challenging task to understand the reversibility of lithium-metal anodes in batteries. Here the authors identify the lithium electrode potential as a critical factor that affects the anode reversibility and subsequently propose an electrolyte design to improve the cycling performance.

Nature Photonics, Published online: 27 October 2022; doi:10.1038/s41566-022-01092-x

Heavy atoms like Cl, Br and I introduced into thermally activated delayed fluorescence chromophores can increase the X-ray absorption cross-section. Light yield of ~20,000 photons MeV–1, detection limit of 45.5 nGy s−1 and imaging resolution of >18.0 line pairs per millimetre is demonstrated.

MPhS-C2 with shortened terminal alkyl chain, features thermal annealing (TA)-insensitive aggregation and condense packing, leading to suppressed upshifts of highest occupied molecular orbital energy level during TA, and efficient charge transport at small phase separation in BTP-eC9 blended devices, obtaining the highest PCE of 17.11% with ΔV _nr of 0.192 V in ASM-OSCs.

Abstract

A critical bottleneck for further efficiency breakthroughs in organic solar cells (OSCs) is to minimize the non-radiative energy loss (eΔV _nr) while maximizing the charge generation. With the development of highly emissive low-bandgap non-fullerene acceptors, the design of high-performance donors becomes critical to enable the blend with the electroluminescence quantum efficiency to approach or surpass the pristine acceptor. Herein, by shortening the end-capped alkyl chains of the small-molecular donors from hexyl (MPhS-C6) to ethyl (MPhS-C2), the material obtained aggregation that was insensitive to thermal annealing (TA) along with condensed packing simultaneously. The former leads to small phase separation and suppressed upshifts of the highest occupied molecular orbital energy level during TA, and the latter facilitates its efficient charge-transport at aggregation-less packing. Hence, the ΔV _nr decreases from 0.242 to 0.182 V, from MPhS-C6 to MPhS-C2 based OSCs. An excellent PCE of 17.11% is obtained by 1,8-diiodoctane addition due to almost unchanged high J _sc (26.6 mA cm⁻²) and V _oc (0.888 V) with improved fill factor, which is the record efficiency with the smallest energy loss (0.497 eV) and ΔV _nr (0.192 V) in all-small-molecule OSCs. These results emphasize the potential material design direction of obtaining concurrent TA-insensitive aggregation and condensed packing to maximize the device performances with a super low ΔV _nr.

Regulation of the configurations of the non-conjugated polymer acceptors enables green solvent-processed large-area binary all-polymer solar cells to achieve record efficiency and robustness. This study not only provides a series of reliable novel conductive materials with excellent performance for flexible wearable solar cells but also elucidates a concept to evaluate the comprehensive performance of organic solar cells.

Abstract

With the great potential of the all-polymer solar cells for large-area wearable devices, both large-area device efficiency and mechanical flexibility are very critical but attract limited attention. In this work, from the perspective of the polymer configurations, two types of terpolymer acceptors PYTX-A and PYTX-B (X = Cl or H) are developed. The configuration difference caused by the replacement of non-conjugated units results in distinct photovoltaic performance and mechanical flexibility. Benefiting from a good match between the intrinsically slow film-forming of the active materials and the technically slow film-forming of the blade-coating process, the toluene-processed large-area (1.21 cm²) binary device achieves a record efficiency of 14.70%. More importantly, a new parameter of efficiency stretchability factor (ESF) is proposed for the first time to comprehensively evaluate the overall device performance. PM6:PYTCl-A and PM6:PYTCl-B yield significantly higher ESF than PM6:PY-IT. Further blending with non-conjugated polymer donor PM6-A, the best ESF of 3.12% is achieved for PM6-A:PYTCl-A, which is among the highest comprehensive performances.

Nature Photonics, Published online: 24 October 2022; doi:10.1038/s41566-022-01088-7

A Fourier-transform waveguide spectrometer is demonstrated by using HgTe-quantum-dot-based photoconductors with a spectral response up to a wavelength of 2 μm. The spectral resolution is 50 cm–1. The total active spectrometer volume is below 100 μm × 100 μm × 100 μm.

Nature Photonics, Published online: 24 October 2022; doi:10.1038/s41566-022-01084-x

One-micrometre-thick OLEDs with low operating voltages of 5.11 V, 3.55 V and 6.88 V at 1,000 cd cm–2 for red, green and blue devices, respectively, and long lifetimes (55,000 h, 18,000 h and 1,600 h, respectively) are realized.

Nature Photonics, Published online: 13 October 2022; doi:10.1038/s41566-022-01083-y

Green OLEDs based on BNSeSe offer high operational efficiency and reduced efficiency roll-off.

Nature Photonics, Published online: 10 October 2022; doi:10.1038/s41566-022-01079-8

A new series of self-assembled Pt(II) complexes with high emission quantum yields enables OLEDs with a maximum emission wavelength of 995 nm and an external quantum efficiency of 4.3%.

Exciton–polaron quenching induced by spontaneous orientation polarization (SOP) is generally quantified and modeled in organic light-emitting devices (OLEDs). Quenching is probed using photoluminescence and engineered by varying electron transport layer SOP through materials selection and dilution with a nonpolar material. This work underscores the significance of SOP-induced quenching in limiting OLED efficiency and provides a means to tune its severity.

Abstract

Many electron transport layer (ETL) materials employed in organic light-emitting devices (OLEDs) show a preferred orientation of the molecular permanent dipole moments. This phenomenon is known as spontaneous orientation polarization (SOP) and results in the formation of bound polarization charge. In an OLED, this leads to the accumulation of polarons (typically holes) at the ETL/emissive layer interface to balance this charge. Previous work on phosphorescent OLEDs has found that exciton–polaron quenching due to SOP-induced hole accumulation can reduce peak efficiency by ≈20%. In this work, the generality of this phenomenon is systematically established by probing polaron accumulation and quenching in phosphorescent OLEDs with varying degrees of SOP. Exciton quenching is quantified by optically probing the photoluminescence of the device emissive layer during operation. It is found that the degree of SOP-induced luminescence quenching and reduction in device efficiency scale directly with ETL SOP. It is further demonstrated that the degree of polarization and amount of quenching can be tuned by mixing the polar ETL with a nonpolar host (dipolar doping). This work establishes a ubiquitous role for SOP in determining OLED efficiency and demonstrates dipolar doping as a means to tune the underlying exciton–polaron quenching.

Nature Photonics, Published online: 13 October 2022; doi:10.1038/s41566-022-01083-y

Green OLEDs based on BNSeSe offer high operational efficiency and reduced efficiency roll-off.

A high-performance and self-powered blue perovskite photodetector (PPD) is developed by designing and optimizing A-site of APb(Br_0.65Cl_0.35)₃ (A = formamidinium (FA⁺), methylammonium (MA⁺), Cs⁺) perovskites (PVSKs). The incorporation of Cs⁺ into FA/MA-PVSKs reduces the lattice strain and defect density. Consequently, a best-performing Cs-incorporating device shows an external quantum efficiency (EQE) of 84.9% which is the highest EQE reported in blue PDs.

Abstract

A self-powered, color-filter-free blue photodetector (PD) based on halide perovskites is reported. A high external quantum efficiency (EQE) of 84.9%, which is the highest reported EQE in blue PDs, is achieved by engineering the A-site monovalent cations of wide-bandgap perovskites. The optimized composition of formamidinium (FA)/methylammonium (MA) increases the heat of formation, yielding a uniform and smooth film. The incorporation of Cs⁺ ions into the FA/MA composition suppresses the trap density and increases charge-carrier mobility, yielding the highest average EQE of 77.4%, responsivity of 0.280 A W⁻¹, and detectivity of 5.08 × 10¹² Jones under blue light. Furthermore, Cs⁺ improves durability under repetitive operations and ambient atmosphere. The proposed device exhibits peak responsivity of 0.307 A W⁻¹, which is higher than that of the commercial InGaN-based blue PD (0.289 A W⁻¹). This study will promote the development of next-generation image sensors with vertically stacked perovskite PDs.

A multi-resonance thermally activated delayed fluorescence (MR-TADF) emitter exhibiting deep-blue emission with Commission Internationale de L'Eclairage coordinates of (0.132, 0.092), narrow full width at half maximum of 22 nm, and high external quantum efficiency of 23.4% is developed by introducing bulky biphenyls and N-biphenyl-N-ortho-dimethylphenylamine that create dense local triplet states and suppress intramolecular aggregation.

Abstract

Multi-resonance thermally activated delayed fluorescence (MR-TADF) molecules based on boron and nitrogen atoms are emerging as next-generation blue emitters for organic light-emitting diodes (OLEDs) due to their narrow emission spectra and triplet harvesting properties. However, intermolecular aggregation stemming from the planar structure of typical MR-TADF molecules that leads to concentration quenching and broadened spectra limits the utilization of the full potential of MR-TADF emitters. Herein, a deep-blue MR-TADF emitter, pBP-DABNA-Me, is developed to suppress intermolecular interactions effectively. Furthermore, photophysical investigation and theoretical calculations reveal that adding biphenyl moieties to the core body creates dense local triplet states in the vicinity of S₁ and T₁ energetically, letting the emitter harvest excitons efficiently. OLEDs based on pBP-DABNA-Me show a high external quantum efficiency (EQE) of 23.4% and a pure-blue emission with a Commission Internationale de L'Eclairage (CIE) coordinate of (0.132, 0.092), which are maintained even at a high doping concentration of 100 wt%. Furthermore, by incorporating a conventional TADF sensitizer, deep-blue OLEDs with a CIE value of (0.133, 0.109) and an extremely high EQE of 30.1% are realized. These findings provide insight into design strategies for developing efficient deep-blue MR-TADF emitters with fast triplet upconversion and suppressed self-aggregation.

Nature Photonics, Published online: 10 October 2022; doi:10.1038/s41566-022-01079-8

A new series of self-assembled Pt(II) complexes with high emission quantum yields enables OLEDs with a maximum emission wavelength of 995 nm and an external quantum efficiency of 4.3%.

This novel, mechanically flexible and bifunctional separator integrates the merits of serving as a highly aligned ion-redistributor to self-regulate/orientate the flux of Na-ions from a chemical molecular level and physically suppresses Na dendrite puncture at a mechanical structural level. Remarkably, Na symmetric cells achieve unprecedented long-term cycling performances at high current densities in additive-free carbonate-based electrolytes.

Abstract

Sodium (Na) is the most appealing alternative to lithium as an anode material for cost-effective, high-energy-density energy-storage systems by virtue of its high theoretical capacity and abundance as a resource. However, the uncontrolled growth of Na dendrites and the limited cell cycle life impede the large-scale practical implementation of Na-metal batteries (SMBs) in commonly used and low-cost carbonate electrolytes. Herein, the employment of a novel bifunctional electrospun nanofibrous separator comprising well-ordered, uniaxially aligned arrays, and abundant sodiophilic functional groups is presented for SMBs. By tailoring the alignment degree, this unique separator integrates with the merits of serving as highly aligned ion-redistributors to self-orientate/homogenize the flux of Na-ions from a chemical molecule level and physically suppressing Na dendrite puncture at a mechanical structure level. Remarkably, unprecedented long-term cycling performances at high current densities (≥1000 h at 1 and 3 mA cm⁻², ≥700 h at 5 mA cm⁻²) of symmetric cells are achieved in additive-free carbonate electrolytes. Moreover, the corresponding sodium–organic battery demonstrates a high energy density and prolonged cyclability over 1000 cycles. This work opens up a new and facile avenue for the development of stable, low-cost, and safe-credible SMBs, which could be readily extended to other alkali-metal batteries.